Solid state lighting emitters are used in a variety of lighting apparatuses in, for example, commercial, automotive, and consumer lighting applications. Solid state emitters can comprise, for example, one or more unpackaged light emitting diode (LED) chips, one or more packaged LED chips, wherein the chips can comprise inorganic and/or organic LED chips (OLEDs). Solid state emitters generate light through the recombination of electronic carriers (electrons and holes) in a light emitting layer or region of an LED chip. LED chips have significantly longer lifetimes and a greater luminous efficiency than conventional incandescent and fluorescent light sources. However, as LED chips are narrow-bandwidth light emitters, it can be challenging to simultaneously provide good color rendering in combination with high luminous efficacy while maintain a maximizing brightness and efficiency.
Incandescent bulbs tend to produce a natural and aesthetically pleasing illumination compared to other types of conventional lighting apparatuses. In particular, incandescent bulbs typically range from a color temperature of about 2700K at full brightness, a color temperature of about 2000K at 5% brightness, and a color temperature of about 1800K at about 1% brightness. This compares favorably with daylight, which varies from about 6500K at midday to about 2500K at sunrise and sunset.
Research indicates that people tend to prefer warmer color temperatures (e.g., approximately 2700K to 3000K) at low brightness levels in intimate settings. LED lighting manufacturers are challenged with providing lighting sources or apparatuses utilizing LED chips to generate light having a color behavior that approximates the behavior of incandescent lighting. Another challenge exists in achieving dimmable color behavior via LED chip based lighting apparatuses that approximate the dimmable characteristics of incandescent lighting.
Conventional lighting systems can be powered via an alternating current (AC) source, however; they typically require a costly AC-DC power converter. To avoid the disadvantages and costs associated with AC-DC power converters, conventional LED chip based lighting sources are configured to operate directly from an AC power source without AC-DC conversion. In conventional driving schemes, some groups of LED chips are powered “on” when the amplitude of the AC waveform is positive, and other groups of LED chips are power “on” when the amplitude of the AC waveform is negative. This results in perceptible flicker and reduced efficiency. A challenge exists in achieving LED chip based light sources configured to operate directly from an AC power source with imperceptible flicker.
Another challenge associated with utilizing LED chips in a lighting source lacking an AC-DC power converter is thermal management, including efficiently dissipating heat generated by LED chips without overheating individual chips (which would shorten LED chip lifetime) and without needlessly increasing heatsink area (which would increase cost and size of a light source).
Accordingly, a need exists for improved solid state lighting apparatuses, systems, and/or improved methods including use and provision of solid state lighting apparatuses that can be directly coupled to an AC voltage signal or AC power, without requiring use of an on-board switched mode power supply. Desirable solid state lighting apparatuses, systems, and methods would exhibit improved light extraction, brightness, and/or improved thermal management. Desirable apparatuses, systems, and methods would also exhibit reduced cost and make it easier for end-users to justify switching to LED products from a return on investment or payback perspective.